Apparatus for hydrolyzing cellulosic material

ABSTRACT

Cellulosic material is converted to ethanol by hydrolyzing the cellulosic material in a gravity pressure vessel (50), and fermenting the product thereof. The gravity pressure vessel (50) employed is adapted to accommodate a continuous hydrolysis reaction and maximize the fermentable product yield on a commercial scale. The gravity pressure vessel (50) employed is also adapted to maximize the thermodynamic efficiencies of the hydrolysis reaction, as well as the entire ethanol producing process.

This application is a division of application Ser. No. 08/644,401, filedMay 1, 1996, now U.S. Pat. No. 5,711,817.

TECHNICAL FIELD

The present invention is generally directed toward a process wherebycellulosic material is converted to ethanol. Specifically, the presentinvention is directed toward an apparatus and method for the hydrolysisof cellulosic material to sugars which may be subsequently fermented.More specifically, the present invention is directed to an apparatus andmethod for the conversion of cellulosic material suspended in a fluidmixture via acid hydrolysis in a gravity pressure vessel.

BACKGROUND ART

Ethanol is a viable, economical, and relatively clean fuel substitute oradditive. It is easily obtained from the fermentation of grain or othersubstances containing sugars and starches. Although grain and othersugar-bearing substances are in abundance, the conversion of cellulosicmaterial, such as found in municipal solid waste, to sugar followed bythe fermentation of the sugar has been found useful for the purpose ofobtaining ethanol. The use of such waste cellulose has been particularlyattractive in the face of higher grain costs and concerns about wastedisposal.

Cellulosic material generally includes waste paper, agricultural chafe,municipal solid waste residual fluff, and wood products. Thesesubstances are converted to sugar via hydrolysis. Heretofore in the art,cellulosic material has been hydrolyzed by first reducing the materialto a pulp and reacting that pulp with sulfuric acid. Upon theintroduction of heat, hydrolysis begins and the cellulosic material isconverted to sugar. The reaction is quenched by rapid cooling of themixture, followed by acid neutralization. Rapid quenching is necessarybecause the hydrolysis reaction is virtually instantaneous, and overexposure to heat and acidic conditions will result in the decompositionof the sugar product thereby reducing yield.

This process, however, is thermally inefficient because the heatintroduced to the system is lost through the rapid cooling of thesystem. Furthermore, inefficiencies resulting from the use of thick pulpsolutions of cellulosic material, which conventionally containsapproximately 20% suspended solids, have been recognized. Specifically,these solutions require screw augers to accomplish the required mixingof acid and heat. Thus, when a reaction vessel is 1,000 cubic feet,which is the minimum for commercial quantities, the time to achieveuniform mixing can be as long as twenty minutes. In addition to theinefficiencies associated with powering the auger, this process willresult in poor sugar yields as the time required to uniformly mix thepulp is typically too long, resulting in the decomposition of theresulting sugar.

Although the problems associated with the use of thick pulps can beovercome by simple dilution with water, the added energy required tohandle such liquid results in further inefficiencies. Indeed, the totalenergy required to produce ethanol via such a process is greater thanthe heat of combustion of the resulting ethanol.

Thus, a need exists to convert cellulosic material to sugar for thepurpose of obtaining ethanol in an efficient manner. Specifically, tocreate an economical fuel substitute or additive, the thermal andchemical inefficiencies associated with the processes of hydrolysisdescribed hereinabove must be overcome.

Numerous methods and reactions for carrying out hydrolysis are known inthe art. For example, Titmas in U.S. Pat. Nos. 3,853,759 and 4,792,408discloses a continuously flowing hydraulic column wherein materialssuspended in water are heated and gravity pressurized to effecthydrolysis. The heated material is forced upward by column pressure andthereby cooled and depressurized. Although this process could handlelarge quantities of cellulosic material, poor net sugar yield would beobtained because there is no means to control or manipulate the lengthof the hydrolysis reaction, nor is there any means to abruptly andspecifically control the quenching of the reaction. To achievesatisfactory sugar yields, the hydrolysis reaction must be stopped partway through the normal coarse of chemical events. This has not beenaccomplished heretofore in the art.

Also, Pavilon, U.S. Pat. No. 5,135,861, discloses a method of producingethanol from an aqueous slurry of biomass. The carbon dioxide resultingfrom fermentation is captured and used to catalyze the hydrolysis of thebiomass. Pavilon, however, fails to efficiently utilize the heat neededfor hydrolysis to catalyze further hydrolysis reactions, and thus theenergy needed to convert the biomass to ethanol is greater than theresulting heat of combustion of the ethanol.

Thus, there remains a need for a method and apparatus for the conversionof cellulosic material to ethanol. Specifically, there remains a needfor a method an apparatus for the efficient hydrolysis of cellulosicmaterials which includes improving sugar yield and capturing the heatneeded for hydrolysis to further additional hydrolysis which will inturn result in a process that is both cost effective andthermodynamically efficient.

DISCLOSURE OF THE INVENTION

It is therefore a primary object of the present invention to provide amethod for the hydrolysis of cellulosic material to sugar.

It is a further object of the present invention to provide a method forthe hydrolysis of cellulosic material, as above, that has improvedchemical and thermal efficiency.

It is still a further object of the present invention to provide amethod for the hydrolysis of cellulosic material, as above, that iscontinuous and capable of hydrolyzing large volumes of cellulosicmaterials.

It is a further object of the present invention to provide a method forthe hydrolysis of cellulosic material, as above, whereby a significantportion of the fluid temperature is internally recovered.

It is another object of the present invention to provide an apparatusfor the hydrolysis of cellulosic materials.

It is yet another object of the present invention to provide anapparatus, as above, that efficiently recovers and utilizes the heatneeded for hydrolysis to initiate further hydrolysis reactions.

It is still another object of the present invention to provide anapparatus, as above, that effectively provides for a predeterminedreaction time and acidity level so as to maximize sugar yield.

At least one or more of the foregoing objects of the present inventiontogether with the advantages thereof over existing methods and apparatusfor hydrolyzing cellulosic materials, which shall become apparent fromthe specification which follows, are accomplished by the invention ashereinafter described and claimed.

In general, the present invention provides a method of hydrolyzingcellulosic material including the steps of processing the cellulosicmaterial into a liquid stream, feeding the liquid stream to the top of ahydraulic downdraft column, conducting the liquid stream from the bottomof the hydraulic downdraft column into a reaction area, heating theliquid stream and lowering the pH of the liquid stream within thereaction area, thereby hydrolyzing the cellulosic material to form sugarwithin the liquid stream, and conducting the liquid stream containingthe sugar from the reaction chamber to the top of a hydraulic updraftcolumn.

The present invention further provides a method of converting cellulosicmaterial to ethanol including the steps of processing the cellulosicmaterial into a liquid stream, reacting the liquid stream within agravity pressure vessel thereby converting the cellulosic material tosugar, and fermenting the sugar thereby forming ethanol.

The present invention also provides an apparatus for hydrolyzingcellulosic material within a continuous liquid stream which includes afirst vertical passageway for receiving the liquid stream near the topthereof. A reaction area communicates with the first vertical passagewayfor receiving the liquid stream near the bottom of the first verticalpassageway. Means are provided for delivering a gaseous material to theliquid stream, and in addition, means are provided for delivering heatto the liquid stream. A second vertical passageway communicates with thereaction area and receiving the liquid stream near the bottom thereofand delivers the liquid stream near the top thereof.

A preferred exemplary apparatus and method for the continuous conversionof cellulosic material to ethanol, which incorporates the concepts ofthe present invention, is shown by way of example in the accompanyingdrawings without attempting to show all the various forms andmodifications in which the invention might be embodied, the inventionbeing measured by the appended claims and not by the details of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the overall process and system forproducing ethanol from cellulosic material.

FIG. 2 is a fragmented vertical, cross-sectional view of a gravitypressure vessel in place within the strata.

FIG. 3 is a sectional view taken substantially along line 3--3 of FIG.2.

FIG. 4 is an isometric view of a portion of the gravity pressure vesselexposing the inner reactor casing.

FIG. 5 is an enlarged vertical, sectional view of the gravity pressurevessel particularly showing the reaction area.

FIG. 6 is a fragmented vertical sectional representation illustrating adevice for inhibiting the excessive feed of a higher density fluid intothe gravity pressure vessel.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

The overall process and system of the present invention is bestdescribed with reference to the schematic representation of FIG. 1. Itshould be understood, for purposes of this disclosure, particularly withregard to the schematic representation, that appropriate pumping devicesand conduits are employed to move material between the various stages ofthe system. It should be further understood that the process whichconverts cellulosic material to ethanol is a continuous process, andtherefore one of ordinary skill in the art will understand that variouspumping devices and storage areas will be employed to maintain theprocess in continuous operation.

In one particular use, source material containing cellulosic material istypically obtained from municipal solid wastes, generally after theextraction of marketable goods. Source material, however, can beobtained from any of a number of sources, including but not limited towaste pulp from paper factories, spent cellulose from paper recycleplants, and refuse from food processing plants. The material obtainedfrom municipal solid wastes is commonly referred to as residual fluffand generally includes paper scraps, lawn wastes, newsprint andcardboard, packaging wastes, wood, and food wastes which are usuallyrich in cellulosic content. Commonly, persons with such materials willpay for its removal.

Source material is delivered from source stream 10 to a water suspensiontank 11 where water is introduced. With the introduction of water, someof the cellulosic material dissolves while some simply forms asuspension in the water, or an aqueous slurry. This mixture will bereferred to hereinafter as the liquid stream. Within suspension tank 11,styrofoam and heavy materials are separated and returned to the sourcestream via 14.

From the water suspension tank 11, the liquid stream is delivered to afiber shredding station 12 where solids are reduced to a common smallsize. When dealing with municipal solid wastes, it is specificallydesirable to shred the solid underwater to preclude explosion ofhazardous materials. This also allows a second opportunity to removeundesirable materials that were attached to the cellulosic material inthe liquid stream. The shredding station 12 may also be adapted toseparate very dense materials, such as steel bottle caps, as well aslight materials such as a styrofoam. These undesirable materials arealso returned to the source stream via 14.

The liquid stream is then received by a density separator 13, such as aclarifier, where gravity separation allows for the separation ofsupernatant materials lighter than water. Such supernatant materialstypically include polyethylene plastics, styrofoam and the like, whichare floated to the top and removed for further processing which caninclude pelletization such as at by-product preparation stage 15.Heavier subnatent materials, mostly cellulosic material, remain in theliquid stream. For purposes of this disclosure, the steps describedabove will generally be referred to as processing the cellulosicmaterial into a liquid stream.

The processed liquid stream is then introduced to a gravity pressurevessel 50 for hydrolyzing cellulosic material. For example, whenmunicipal solid wastes are employed, the liquid stream delivered fromthe shredding station 12 typically includes about five percent solids,and following density separation at 13 the liquid stream is concentratedto about nine percent or more suspended solids.

Within the gravity pressure vessel 50, which will hereinafter bedescribed in more detail, the liquid stream is subjected to properconditions for carrying out acid hydrolysis. This hydrolysis converts asignificant portion of the cellulosic materials to sugars. It should beappreciated that the resulting sugars become part of the liquid streamfollowing hydrolysis. For purposes of this description, the term sugarswill generally refer to those products resulting from the acidhydrolysis of cellulosic materials, typically definable as sugars andstarches and derivatives thereof. It should be appreciated, however,that a very broad spectrum of resultant materials may result fromhydrolysis, even when closely controlled feed stocks are employed. Thus,when viewed in light of the fact that a source stream of the presentinvention could include more than 10,000 identifiable materials, manyforms of sugars or starches are possible. When converting municipalsolids wastes, the acid hydrolysis will yield a weak solution containingapproximately 3.5 percent to approximately 5 percent sugar, which willproduce a weak beer in fermentation.

The liquid stream, now containing an aqueous sugar solution, isdelivered to a post treatment clarifier, such as density separator 20.Within this clarifier, heavy refractory cellulose, lime, gypsum andinert precipitates are removed. These materials are forwarded to adewatering or carbonate preparation process 21 where the water, whichcontains sugar, is removed and returned to the liquid stream atseparator 20. The solids, which can generally be defined as carbonateswith some sulfates and mud, are stored at carbonate storage 22 forfuture commercial use.

The aqueous sugar solution, which also contains residual particles ofunreacted cellulose, is delivered from separator 20 to a fermentationapparatus 23, which typically includes several tanks. Not shown arecertain heat exchangers that may be necessary to precondition theaqueous sugar stream. This preconditioning generally includes extractingfurfural and other fermentation inhibitors known to those skilled in theart. Fermentation at apparatus 23 generally involves the introduction ofconventional beer yeasts, and the maintenance of active moderateagitation, atmospheric pressure, and a temperature in the range of about70° F. to about 100° F. Maximum sugar yield typically occurs within thetime duration of about 24 to about 36 hours, with variations in time, aswell as temperature, depending on the selection of yeast and otherstimulating additives such as enzymes.

The products of fermentation are ethanol and carbon dioxide, produced in1:1 ratio as generally understood by those skilled in the art. Thecarbon dioxide is captured from fermentation apparatus 23 and directedto a cleaning station 24, such as a condensor. Here, the carbon dioxidecan be condensed under pressure and cooled for purification. Thepurified liquid carbon dioxide is delivered to an evaporator 25 andstored at a metering station 26 for future use in the hydrolysis of thecellulosic material at gravity pressure vessel 50, or elsewhere in theprocess as needed. Generally, when municipal solid wastes are employedas source material, about 80 percent of the acidification needs forhydrolysis are satisfied using carbon dioxide produced duringfermentation.

Because the fermentation of the sugar took place in an aqueous solution,commonly referred to as beer, the resulting ethanol remains in aqueoussolution. This beer is delivered to a dissolved gas floatation station27. Here, particulate impurities suspended in the solution are removed.These impurities include, but are not limited to, living organisms,dust, yeast and cellulose. Removal of such particulate impuritiestypically includes dissolving the carbon dioxide, or any gas such asair, in water under pressure. This solution is flash mixed with the beerin an atmospheric tank. As the dissolved carbon dioxide precipitatesfrom the mixture, it attaches to nucleic bubble formation on the surfaceof the suspended solids. The combined bubble and suspended solid, nowlighter than water, is floated to the surface.

The separated particles are conveyed to a biomass recycle station 28where the yeast is tested and verified for seeding the fermentationprocess, and the remainder conveyed to an excess biomass preparationstation 29 for conventional dewatering and shipment as a proteinsupplement for animal feed. The remaining liquid from the dewateringprocess is returned to the liquid stream.

The purified aqueous ethanol solution, or beer, is delivered to a beerstorage station 30. When distillation of the ethanol is desired, thesolution may be pre-heated by a heat exchanger 31 and then received by avacuum distillation column or columns 32. This can be any form ofdistillation and typically requires external heat from a source such assteam. After primary distillation at columns 32, the distillate istransferred to a secondary separation apparatus 34 where residualorganics are typically removed. Apparatus 34 could include, but is notlimited to, engineered zeolite, reverse osmosis, or extraction andconcentration using ice crystallization. It has been found that the useof evaporation to accomplish this secondary separation is far toomechanically and energy intensive to be economical or efficient.

The distillate is ethanol that is approximately about 95% to about 99%pure, or greater than 193 proof as commonly understood in the art.Further, the distillate can be dehydrated to achieve 199.5 proof. Thisdistillate is cooled and delivered to either an awaiting transportvehicle or storage tank. The spent aqueous solution, on the other hand,is cooled and delivered a recycle station 35. It should be noted thatthe cooling of both the purified ethanol and the spent aqueous solutioncan occur within a heat exchanger, such as 31, which is preferably acounterflow heat exchanger. Thus, heat from distillation process 32 isused to preheat the fluid stream of ethanol, i.e. beer, prior todistillation.

At recycle station 35, the spent water is tested. Based on the qualityof the water, the spent aqueous solution is recycled back to the systemto suspend incoming cellulosic material at water suspension tank 11, ortreated at an on-site waste water treatment plant 36. After treatment at36, the water may be diverted to a publicly owned treatment works orused at tank 11. The treatment plant 36 should be capable of processing72,000 gallons per day, with a net water discharge to the publicly ownedtreatment works preferably as low as 10,000 gallons per day.

On-site treatment plant 36 can include a conventional waste activatedsolids extended aeration biological waste water treatment plant whereinexcess nitrates are removed prior to discharge to a publicly ownedtreatment works.

As previously described, the liquid stream of cellulosic material ishydrolyzed in gravity pressure vessel 50. This apparatus is bestdescribed with reference to FIGS. 2 & 3. A tubular casing 52 ispositioned in the strata S in a bore within the earth. Casing 52 can beseparated from strata S with a grout to control the intermixing offluids that may be present in the strata, to reduce the heat losses fromthe apparatus, and to protect the casing 52 from adverse corrosiveeffects of strata S. Optionally, a surface casing 51 may be employed,which is an additional tubular member encompassing strata casing 52 forthe purpose of protecting water aquifers during drilling of the longstring chamber bore hole.

Concentric within and spaced from casing 52 is an outer reactor tubularcasing 53 having lower closed end 54. The space between casings 52 and53 forms an isolating annulus 55 that acts as a mutual barrier toprotect the strata from the process and to protect the process from thestrata. Such isolation may be enhanced by evacuating annulus 55 to alower pressure, such as to approximately one thousandth of anatmosphere. Under such conditions, the integrity of casings 52 and 53will be verified and heat loss to the strata from the apparatus will begreatly reduced, as will the corrosive effects on the surfaces of bothcasing 52 and outer reactor casing 53. A closed and sealed drop tube 80can be positioned in annulus 55 to house thermocouples to monitortemperature conditions within annulus 55, as well as within the outerreactor casing 52.

Concentric within and spaced from the outer reactor casing 53 iscounterflow tubular casing 56. The space between outer reactor casing 52and counterflow casing 56 forms outer reactor annulus 57. The liquidstream containing cellulosic material, which enters the apparatus atinlet 58, is caused to descend to a zone of higher pressure within outerreactor annulus 57. This pressure results from the cumulative weight ofthe fluid, as well as from residual pressures from fluid handling pumps.Thus, annulus 57 essentially is a vertical passageway or hydraulicdowndraft column that receives the liquid stream and delivers the streamto the bottom of gravity pressure vessel 50. The bottom of counterflowcasing 56 can be modified with an outward flare 59 to assist theinduction of recirculation of the liquid stream near the bottom ofannulus 57, and produce a more uniform feed as the liquid moves throughthe reaction vessel.

As is best shown in FIG. 3, concentric within and spaced from thecounterflow casing 56 is carbon dioxide input tube 60 which essentiallyis a means for delivering gaseous material to the bottom of vessel 50via carbon dioxide annulus 68. Carbon dioxide is delivered to the lowerclosed end 54 of reaction vessel 50 through input tube 60 from itsdischarge point at 61 as shown in FIG. 2.

Referring again to FIG. 3, concentric within and spaced from input tube60 is a tubular steam pipe 62 which represents a means for deliveringheat to the bottom of vessel 50. Steam pipe 62 is concentrically nestedwithin an outer tubular housing 63, whereby steam pipe 62 and outerhousing 63 form annulus 64 which may be insulated or evacuated toprevent the premature loss of heat from steam pipe 62. Steam pipe 62delivers heat energy, on an as needed basis, to the reactor vessel 50from its discharge point at 67 to the region generally defined by thelower closed end 54 as shown in FIG. 2.

The space between carbon dioxide input tube 60 and counterflow casing 56forms inner reactor annulus 65, which defines a second verticalpassageway or hydraulic updraft column. The liquid stream containingcellulosic material, which descends down outer annulus 57, subsequentlyascends up inner annulus 65 and out of the reactor vessel 50 throughoutlet 66. The forces driving this ascension, as well as the reactionstaking place to the cellulosic material as it ascends, will be describedin greater detail hereinafter.

As is best depicted in FIG. 2, the gravity pressure vessel is cappedwith device 40. Generally device 40 will serve to seal the annuli ofreactor vessel 50 from the atmosphere, thereby maintaining the desiredpressure or vacuum. As is generally shown, device 40 can be equippedwith the inlet 58 and the outlet 66 previously described, although thoseof ordinary skill in the art will be able to modify the device 40, basedon the teachings herein. Of course, device 40 is able to accommodatevarious feed pipes and housings for analytical devices, which will bothbe described hereinafter and which one or ordinary skill may findnecessary to achieve the objects of this invention based on theteachings herein.

To a portion of the vertical length of carbon dioxide input tube 60there is removably attached an inner reactor casing generally indicatedby the numeral 70. More specifically, inner reactor casing 70 isremovably attached to and circumscribes a portion of input tube 60. Itshould be appreciated that, with inner reactor casing 70 attached totube 60, the shape of annulus 65 is modified. This modified area ofannulus 65 essentially creates and defines a reaction area.

Inner reactor casing as generally indicated by the numeral 70 is bestdescribed with reference to FIG. 4. In the preferred embodiment, innerreactor casing 70 generally includes three venturi sections that arepositioned along the same vertical axis with respect to the length ofthe carbon dioxide input tube 60. The first venturi section 71 generallyincludes two oppositely directed frustums connected at their bases,which circumscribe the carbon dioxide input tube 60. As a result of thisconfiguration, the inner annulus 65 is reduced at the junction of thetwo bases 72.

The second venturi section 73, which is positioned above and connectedto the first venturi section 71, generally includes two oppositelydirected frustums having a generally cylindrically shaped member 74connected therebetween. Cylindrical member 74 preferably has the samediameter as the bases of the frustums, and the bases of each frustum areconnected to member 74. The frustums and the cylindrical membercircumscribe the carbon dioxide input tube 60. As a result of thisconfiguration, the inner annulus 65 is reduced at the junction of thebases and cylindrical member, and remains reduced throughout thevertical length of member 74. As is particularly the case with member74, the length and configuration of the inner reactor casing 70 can bemodified. For example, reactor casing 70 can be removed and member 74can be modified in length. This is typically accomplished by replacingit with a longer member or by simply adding additional members, similarto 74, between the frustums of the second venturi section. In turn,lengthening member 74 will increase the length of the reduced portion ofannulus 65.

The third venturi section 75, which is positioned above and connected tothe second venturi section 73, generally includes two oppositelydirected frustums connected at their bases 76. The frustums circumscribethe carbon dioxide input tube 60. As a result of this configuration, theinner annulus 65 is reduced at the junction of the two bases 76.

It should be understood that while the inner reactor casing has beendescribed with reference to the preferred embodiment, the inner reactorcasing can be any means that serves to reduce and expand the width ofinner annulus 65 in a manner generally consistent with that described inthe preferred embodiment. Specifically, based on the teachings herein,one skilled in the art should be able to design numerous configurationsthat serve to alter the flow rate of fluid as it travels up annulus 65.

Also represented in FIG. 4 are an acid feed pipe 81 and a caustic feedpipe 82. In the preferred embodiment, acid feed pipe 81 supplies acid toan acid feed collar 83, which is generally positioned at the junction offirst and second venturi sections. From acid feed collar 83, acid can bedispersed throughout inner annulus 65 in the region generally adjacentto feed collar 83. Caustic feed pipe 82 supplies caustic to a causticfeed collar 84, which is generally positioned at the junction of secondand third venturi sections. From caustic feed collar 84, causticsolution can be dispersed throughout inner annulus 65 in the regiongenerally adjacent to feed collar 84. It should be understood that anymeans of delivering acid and caustic to the above defined regions can beemployed for purposes of this invention. Further shown in FIG. 4 isthermocouple tubular housing 85, which may be employed to monitor thephysical and chemical characteristics of the continuously flowing fluidswithin reactor vessel 50.

The apparatus as just described is highly useful to perform the processof converting cellulosic material to sugars for the subsequentconversion to ethanol. As previously described, the term sugars isgenerally meant to refer to those products resulting from the acidhydrolysis of cellulosic materials. This conversion occurs via chemicalreactions taking place within vessel 50 as cellulosic material,dissolved or mixed within an aqueous stream, continuously flows throughthe vessel.

The hydrolysis of cellulosic material is now best described withreference to FIG. 5. Steam, which is pumped down steam pipe 62, isintroduced to the process and heats the stream of fluid in the region90, generally defined as that region near the lower closed end 54 ofreactor casing 53. Moreover, once the vessel is in continuous operation,heat resulting from acid hydrolysis reactions taking place in reactionregions 92 and 93, as will later be explained, migrates throughcounterflow casing 56 to heat the fluid stream as it descends down outerreactor annulus 57. Thus, steam from pipe 62 is delivered only on an asneeded basis; that is, to compensate for that portion of downflowingfluids insufficiently preheated though counterflow 56. It is noteworthythat a maximum amount of heat energy can be recaptured by introducingthe steam in the region 90.

It should be appreciated that the heat needed to drive a hydrolysisreaction of cellulosic material is generally greater than 200° C. andpreferably in the range between about 260° C. and about 290° C. Thegreater the temperature, the less acid is needed to drive the reaction.At too great a temperature, however, the hydrolysis reaction is noteasily controlled, and, therefore, results in the decomposition of thesugar product. Thus, based on the teachings herein, one of ordinaryskill in the art will be able to alter the temperature and acidity levelto achieve optional results. Of course, the constantly changing feedstream will also factor into the optimal temperature and acidity sought.It should further be appreciated that the pressure experienced by theliquid stream within the gravity pressure vessel increases as the liquidstream approaches the bottom of the vessel. This increased pressure,which is generally in the range of between about 600 psi and about 1200psi, and preferably between about 800 psi and about 1000 psi, furtherserves to drive the hydrolysis reaction.

Because of the pressure resulting from the height of the liquid streamdescending down outer reactor annulus 57, and the reduction in thedensity of the fluid resulting from the introduction of carbon dioxide,the liquid stream is caused to ascend up inner reactor annulus 65, aportion of which has been modified to define a reaction area asdescribed hereinabove. For purposes of explaining the hydrolysis of thecellulosic material ascending up through the reaction area, the reactionarea will be defined in terms of six regions. The first region 91 isgenerally defined as that region of annulus 65 below point 72 of firstventuri section 71. At or near first reaction region 91 is the areawhere carbon dioxide input tube 60 terminates at 61, thereby introducingthe carbon dioxide to the liquid stream in region 91. It should also benoted that the carbon dioxide is preheated prior to its entry in theprocess as a result of steam pipe 62 being concentric and within carbondioxide input tube 60. The carbon dioxide forms carbonic acid within theliquid stream thereby lowering the pH and catalyzing the hydrolysisreaction. It is preferred that enough carbon dioxide be added to theliquid stream to bring the pH of the solution below 5.0 and preferablybelow 3.5.

The preheated liquid stream, now containing sufficient carbon dioxide,continues to ascend up annulus 65 and encounters the second reactionregion 92 where the flow of the fluid stream is restricted due to firstventuri section 71. The liquid stream's contact with venturi section 71creates a minor shock wave in the passing fluid that is a source ofinstantaneous mixing of the fluid and suspended particles.

Moving upward through annulus 65, the fluid stream next enters thirdreaction region 93. Region 93 is generally defined as the area withinannulus 65 adjacent to or near the junction of first venturi section 71and second venturi section 73. Within region 93, acid is introduced tothe system from a device such as acid feed collar 83, to achieve a pH inthe range of about 2.0 to about 3.0, which carries out hydrolysis of thecellulosic materials. While it is believed that any mineral acid willserve to lower the pH as sought in the present invention, sulfuric acidhas been found to work particularly well and is preferred. It isnoteworthy that such acid is only needed when the pH is insufficientlylowered by the introduction of carbon dioxide to the liquid stream.

As acid hydrolysis reactions convert the cellulosic material to sugars,the fluid steam continues up annulus 65 and enters forth reaction region94. Region 94 is generally defined as the area within annulus 65adjacent to and reduced as a result of cylindrical member 74 of secondventuri section 73. Region 94 is restricted to increase the flow rate ofthe fluid stream undergoing acid hydrolysis, thereby limiting the timein which hydrolysis takes place. As previously described, extended acidhydrolysis of the cellulosic material beyond the required time willdestroy the sugars that are sought from the reaction. Typically, it willtake about 2 to about 4 seconds for the fluid stream to ascend throughregion 94. Because the reaction time is critical and may vary on severalfactors including the nature of the feed stock, the length of region 94,and therefore the reaction time, can be changed. This is accomplished byadding or removing sections of tube 74 as was described hereinabove.

Moving rapidly through region 94, the fluid stream then ascends into thefifth reaction region 95. Region 95 is generally defined as the areawithin annulus 65 adjacent to or near the junction of second venturisection 73 and third venturi section 75. Within region 95, causticsolution, such as calcium hydroxide, is introduced via a device such ascaustic feed collar 84. The introduction of caustic solution raises thepH to approximately 7.5 or greater, thereby quenching the acidhydrolysis reaction. The introduction of a neutralizing agent such ascalcium hydroxide further results in the formation of precipitants suchas calcium carbonate and calcium sulfate. To prevent the fouling of theannuli walls, seed powders of these precipitates can be added with thecaustic solution to the stream, causing the formation of largerprecipitate particles that can be later removed. It should be understoodthat any caustic solution can be introduced which will neutralize thestream of liquid, thereby quenching the hydrolysis reaction, so long assuch caustic solution is not deleterious to the sugar product or liquidstream.

Ascending toward the top of reactor vessel 50, the fluid stream is againrestricted in sixth reaction region 96 due to third venturi section 75is which creates shock wave mixing. Continuing to move upward from thisregion, the fluid ascends unrestricted up the remainder of annulus 65and eventually reaches the top of the reactor vessel 50 where it exitsthe vessel at outlet 66.

As should be evident to one of ordinary skill in the art, the reactiontime is a function of the rate of flow of the liquid stream throughvessel 50. In other words, the reaction time is dictated by the time ittakes the stream to move through the reaction area. Generally, thestream will pass through the reaction area within about 3 seconds toabout 6 seconds.

It should be appreciated that the quenching of the hydrolysis reactionis achieved solely by the neutralization of the fluid stream. Thus, theheat introduced at the bottom of the reaction vessel at region 90remains in the fluid or migrates through casing 56 and heats thedownward flowing input stream. It should further be appreciated that asthe fluid ascends unrestricted up the remainder of annulus 65 toward thetop and the reactor vessel 50, at least 80 percent, and more preferably90-95 percent of the heat introduced via the steam at or near region 90is captured, i.e., migrates through casing 56, or into one of thevarious feed pipes. In other words, the heat introduced to the reactionvessel is recycled within the gravity pressure vessel.

Also depicted in FIG. 5, counterflow casing 56 can be fitted with aliner 79. Although casing 56 has mechanical strength, liner 79 is reliedon for resistance from chemical attack and erosional complications.

Referring again to FIG. 4, it has been discovered that the introductionof acid through acid feed pipe 81 and feed collar 83 could beproblematic because the density of the acid can be up to approximately35 percent greater than the density of hot water and the acid feed pipeis typically about 2,000 feet long. If this weight is left to act onlyagainst the frictional forces within feed pipe 81, the flow rate of theacid will exceed the required delivery rate of acid. Thus, because theaccumulated pressure at the bottom of feed pipe 81 is excessive,irregularities in the discharge of the acid into the reaction region 93could occur. To eliminate this potential problem, it is preferred toemploy an arrangement, such as illustrated in FIG. 6.

This arrangement will be referred to as a vacuum compensated feed.Generally, this arrangement includes acid feed pipe 81 modified with atleast one taper 88, such that the diameter of the acid feed pipe issmaller below the taper than above the taper.

The rate of acid feed is controlled by pump and valving 86. The acid isadmitted into acid feed pipe 81 in a downwardly tangential manner so asto form a falling film 87 that simply wets the inner surface of pipe 81.

As the acid film 87 flows downward, it will eventually flood the entireinner diameter of feed pipe 81, such as at taper 88, and create a columnof acid within pipe 81 below point 88. In other words, the height of thecolumn of acid is generally equivalent to the height of the acid feedpipe below the taper. A vacuum is drawn, using evacuation vane pump 89on the area above the acid column not occupied by the downward flowingfilm 87. Thus, the pressure at the bottom of feed pipe 81 is only theweight of the acid column, typically from taper 88 down to the feedcollar 83. It is, therefore, desirable to modify acid feed pipe 81 withtaper 88 such that the length of acid feed pipe 81 below taper 88 willcreate a pressure at the bottom of acid feed pipe 81 equivalent orapproximate to the pressure within annulus 65, and more specifically,reaction region 93. It should also be appreciated that the rate of acidfeet can be used to manipulate the height of the acid column.

For example, when sulfuric acid is employed, about one pound per squareinch for every 1.9 feet of height is achieved. Water, on the other hand,is about one pound per square inch for every 2.1 feet of height. Thesevalues were calculated after compensating for the loss of density due tofluid expansion that results from rising temperatures as the fluids movedownward in the reaction vessel 50. Based on a vessel 2000 feet deep,which is typical for mild acid hydrolysis reactions, the water pressurewould be approximately 952.4 psi, while that of the acid would beapproximately 1,052.6 psi. This difference causes acid delivery problemswhich are enhanced by the fact that the acid frictional forces are lessthan that of the water.

To alleviate this problem, taper 88 is created so that the distancebetween taper 88 and feed collar 83 is 1810 feet, thereby providing fora column of acid approximately 1810 feet. Thus, approximately 190 feetof the feed pipe is maintained under vacuum.

It should be appreciated that the height and diameters of each annuluswithin reactor vessel 50 are not critical, so long as the height anddiameters are sufficient to achieve the goals of the present invention.Namely, the height must be such that sufficient pressure is achieved atthe bottom of the reactor to drive an efficient hydrolysis reaction.Further, the height must be such that sufficient travel of theup-flowing fluid is achieved so that the heat needed for the hydrolysisreaction can be recycled into the down-flowing fluids through casing 56in an efficient manner.

The diameter of the annuli is typically a function of the make-up of thefeed stream as well as the reaction sought. Typically, the diameter ofthe entire vessel is greater when cellulosic material is converted tosugar than in other gravity pressure vessels. As discussed herein,however, the inner annulus 65 has a reduced diameter at certain points.

A preferred gravity pressure vessel according to the present inventionwill have a height from about 1800 feet to about 2200 feet. The diameterof outer reactor casing 53 is preferably about 24 inches to about 30inches, and the diameter of counterflow tubular casing 56 is preferablyabout 18 inches to about 24 inches.

As with the size of the reactor, the fluid throughput of the reactor isa function of the characteristics of the feedstock. Ideally, the gravitypressure vessel of the present invention will process from about 500 toabout 1000 gallons per hour of fluid stream, which typically comprisesfrom about 5 percent to about 9 percent cellulosic material.

Further details of the pretreatment and post-treatment of the fluids andthe treated products of the process and other materials of construction,proportions, cleaning, corrosion and erosion control, catalysts,alternative acids, vent extraction and control of volatile organiccompounds, stress strain control, expansion compensation, and the like,would all be known to one normally skilled in the art and are notdescribed herein.

It should thus be evident that the method and apparatus disclosed hereinis capable of sustaining conditions amenable to the practical hydrolysisof cellulosic materials in commercial quantities, as the energy demandsinvolved in pressurization and heating are significantly recovered fromthe process stream and not lost to mechanical forces. Further, theby-products of cellulose hydrolysis are fully contained providingoptions for their processing and environmentally safe use or control. Assuch, the objects of the present invention are fully accomplished. Itis, therefore, to be understood that any variation evident falls withinthe scope of the claimed invention and, thus, the selection of specificcomponent elements can be determined without departing from the spiritof the invention herein disclosed and described. For example, the sizeof the gravity pressure may be altered, as can the position andconfiguration of the reaction area. Thus, the scope of the inventionshall include all modifications and variations that may fall within thescope of the claims.

I claim:
 1. An apparatus for hydrolyzing cellulosic material within acontinuous liquid stream comprising a first vertical passageway forreceiving the liquid stream near the top thereof, a reaction areacommunicating with said first vertical passageway near the bottomthereof, means for delivering a gaseous material to the liquid stream,means for delivering heat to the liquid stream, means for delivering amineral acid to said reaction area, means for delivering causticsolution to said reaction area, a second vertical passagewaycommunicating with said reaction area for receiving the liquid streamnear the bottom thereof and delivering the liquid stream near the topthereof, and means for reducing and expanding the width of said secondvertical passageway, thereby altering the flow rate of the liquid streamas it is delivered to the top of said second vertical passageway so asto be conducive to initiating and rapidly quenching a hydrolysisreaction.
 2. An apparatus according to claim 1, wherein said means fordelivering heat to the liquid stream delivers heat near the bottom ofsaid first vertical passageway.
 3. An apparatus according to claim 2,wherein said means for delivering heat delivers steam.
 4. An apparatusaccording to claim 2, wherein said reaction area is a verticalpassageway defined within the lower portion of said second verticalpassageway.
 5. An apparatus according to claim 1, wherein said means fordelivering gaseous material to the liquid stream delivers gaseousmaterial near the bottom of said reaction area.
 6. An apparatusaccording to claim 5, wherein said means for delivering gaseous materialdelivers carbon dioxide.
 7. An apparatus according to claim 1, whereinsaid means for delivering a mineral acid includes a pipe having at leastone taper therein such that the diameter of said pipe is smaller belowsaid taper than above said taper, whereby upon the downward tangentialintroduction of acid within said pipe there will be an acid columnwithin said pipe generally equivalent in height to the height of saidacid feed pipe below said taper.
 8. A gravity pressure vessel forconverting cellulosic material to sugar comprising:a tubular casing; anouter reactor tubular casing positioned within said tubular casing andhaving a lower closed end, whereby said tubular casing and said outerreactor tubular casing form an insulating annulus; a counterflow tubularcasing positioned within said outer reactor tubular casing, whereby saidcounterflow tubular casing and said outer reactor tubular casing form afirst vertical passageway; a carbon dioxide input tube positioned withinsaid counterflow tubular casing, whereby said carbon dioxide input tubeand said counterflow tubular casing form a second vertical passageway; atubular steam pipe positioned within said carbon dioxide input tube; aplurality of venturi sections, each positioned along said carbon dioxideinput tube and extending within the second vertical passageway, therebyselectively restricting the area within the second vertical passageway;an acid feed pipe for delivering an acid to the second verticalpassageway, said pipe including at least one taper; and a caustic feedpipe for delivering a caustic material to the second verticalpassageway.
 9. A gravity pressure vessel according to claim 8 whereinsaid plurality of venturi sections includes first, second and thirdventuri sections.
 10. A gravity pressure vessel according to claim 9further comprising an acid feed collar positioned at the junction ofsaid first and second venturi sections, said acid feed collarcommunicating with said acid feed pipe.
 11. A gravity pressure vesselaccording to claim 9 further comprising a caustic feed collar positionedat the junction of said second and third venturi sections, said causticfeed collar communicating with said caustic feed pipe.